Plate locking mechanism

ABSTRACT

A plate locking mechanism for a surface preparation device comprising a connecting plate having a receiving aperture, a base plate and a floating plate capable of being substantially aligned with the base plate. A fastener extends through a floating plate aperture and engages with a base plate aperture and a resilient member is operatively associated with the fastener to maintain the floating plate in contact with the base plate and wherein, when the base plate is located within the receiving aperture, the floating plate is rotatable to retain the connecting plate in position.

FIELD OF THE INVENTION

The present invention relates to the field of mechanical lockingmechanisms. More particularly, this invention relates to a plate andassociated plate locking mechanism for a surface preparation device.

BACKGROUND OF THE INVENTION

Surface preparation techniques are commonly used to give a desiredfinish to a surface in both home and work environments. Common examplesare the fine sanding of wooden floors and the grinding and perhapssubsequent polishing of concrete floors to give a smooth andaesthetically appealing finish.

Typically, mechanised surface preparation devices are used for suchtasks since large surface areas need to be prepared. Such devices arewell known and generally take the form of either hand held devices withsingle grinding discs, such as an orbital sander, or larger deviceswhich are controlled by an operator pushing them along and which mayhave a number of grinding discs or like preparation tools allowing alarger surface area of floor or other surface to be appropriatelyfinished in a shorter time period.

These larger devices generally have a rotatable plate which is rotatedby a drive shaft and onto which are attached one or more surfacepreparation discs. The surface preparation discs may rotate relative tothe rotatable plate and contact and add the desired finish to thesurface to be prepared. The rotatable plate must be held in place bysome form of holder or locking mechanism.

One example of such a large surface preparation device is a concretegrinder/polisher. These are typically very heavy machines which arefurther weighed down by the inclusion of weights, either on the housingor built into the machine itself, to increase the grinding/polishingforce. This makes it difficult to transport the device and also requiresa certain amount of physical strength from the operator to force thedevice to move in the desired manner from side to side in a sweepingmotion during operation. Control of the device during grinding/polishingis crucial as the high operating speeds of the grinding discs mean thatany unwanted movements can result in gouging of the surface beingprepared and fine control of the machine when encounteringirregularities on the surface being prepared is necessary to prevent asimilar result.

There is a need for a surface preparation device which can more easilybe controlled during operation and which effectively and efficientlyprepares surfaces such as concrete and wooden floors.

Accordingly, it is an aim of the present invention to overcome oralleviate at least some of the disadvantages of current surfacepreparation devices and otherwise to provide consumers with a moreconvenient choice.

SUMMARY OF THE INVENTION

The present invention provides for a plate locking mechanism andreciprocating plate for use in releasably attaching a rotatable plate,the rotatable plate having one or more surface preparation toolsattached, to a surface preparation device.

In one form, although it need not be the only or indeed the broadestform, the invention resides in a plate locking mechanism for a surfacepreparation device comprising:

-   -   (a) a base plate having a base plate aperture;    -   (b) a floating plate capable of being substantially aligned with        the base plate, the floating plate having a first surface, an        actuator and a floating plate aperture, the first surface in        contact with the base plate;    -   (c) a fastener extending through the floating plate aperture and        engaging with the base plate aperture; and    -   (d) a resilient member operatively associated with the fastener        and in contact with a second surface of the floating plate, the        resilient member capable of generating a force on the second        surface of the floating plate to maintain the first surface of        the floating plate in contact with the base plate;

wherein, rotation of the actuator results in relative movement of thefloating plate and the base plate to enable locking of a plate.

Preferably, the base plate is adapted to attach to an underside of thesurface preparation device.

In a further form the invention resides in a plate locking mechanism fora surface preparation device comprising:

-   -   (a) a connecting plate having a receiving aperture and at least        one blocking member;    -   (b) a base plate having a base plate aperture, the base plate        having a shape complimentary to that of the receiving aperture;    -   (c) a floating plate capable of being substantially aligned with        the base plate, the floating plate having a first surface, at        least one floating plate projection and a floating plate        aperture, the first surface, in use, in contact with the base        plate;    -   (d) a fastener extending through the floating plate aperture and        engaging with the base plate aperture; and    -   (e) a resilient member operatively associated with the fastener        and in contact with a second surface of the floating plate to        maintain the first surface of the floating plate in contact with        the base plate;

wherein, when the base plate is located within the receiving aperture,the floating plate is rotatable to align the at least one floating plateprojection with the at least one blocking member to thereby lock theconnecting plate in position.

In yet a further form the invention resides in a plate locking mechanismfor a surface preparation device comprising:

-   -   (a) a floating plate having an actuator, at least one floating        plate projection and a floating plate aperture;    -   (b) a fastener extending through the floating plate aperture,        the fastener having a head and a shank and being adapted to        engage a base plate;    -   (c) a resilient member at least partially surrounding the shank        and extending between the head of the fastener and a receiving        surface of the floating plate;

wherein, moving the head of the fastener towards the receiving surfaceof the floating plate compresses the resilient member.

In still a further form the invention resides in a method of retaining aconnecting plate on a surface preparation machine including the stepsof:

-   -   (a) connecting a floating plate to a base plate using a        fastener, the base plate being attached to an underside of the        surface preparation machine, the floating plate and base plate        being capable of being substantially aligned, the floating plate        having at least one floating plate projection and the fastener        being operatively associated with a resilient member which is        maintained in a partially compressed state by the fastener;    -   (b) locating a connecting plate to surround the base plate, the        connecting plate having a receiving aperture and at least one        blocking member, the receiving aperture being complimentary in        shape to the aligned floating plate and base plate;    -   (c) rotating the floating plate to align the at least one        floating plate projection with the at least one blocking member        to thereby retain the connecting plate.

In yet still a further form the invention may reside in a rotatableplate for a surface preparation device comprising a plate collardefining a hollow passage, the plate collar extending generallyperpendicularly from the plane of the rotatable plate and ending in aconnecting plate, the connecting plate in a plane parallel to that ofthe rotatable plate and having a receiving aperture continuous with thehollow passage

Further features of the present invention will become apparent from thefollowing detailed description.

Throughout this specification, unless the context requires otherwise,the words “comprise”, “comprises” and “comprising” will be understood toimply the inclusion of a stated integer or group of integers but not theexclusion of any other integer or group of integers.

BRIEF DESCRIPTION OF THE FIGURES

In order that the invention may be readily understood and put intopractical effect, preferred embodiments will now be described by way ofexample with reference to the accompanying figures wherein likereference numerals refer to like parts and wherein:

FIG. 1 is a perspective view of the underside of a surface preparationdevice employing a plate locking mechanism according to an embodiment ofthe invention;

FIG. 2 is an exploded view of the components of a plate lockingmechanism, according to an embodiment of the invention, with associatedrotatable plate and accessories;

FIG. 3 is a perspective view of a plate locking mechanism according toan embodiment of the invention;

FIG. 4A is a perspective view of a plate locking mechanism, according toan embodiment of the invention, when in the unlocked/removalconfiguration;

FIG. 4B is a perspective view of a plate locking mechanism, according toan embodiment of the invention, when in the locked/operationalconfiguration;

FIG. 5 is a perspective view of a plate locking mechanism according to afurther embodiment of the invention;

FIG. 6 is a perspective view of a plate locking mechanism according toyet a further embodiment of the invention; and

FIGS. 7A to 7D are plan views of a number of alternative designs for usein forming a plate locking mechanism according to various embodiments ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The plate locking mechanism embodiments which are discussed herein aredescribed in relation to their use in a concrete grinder/polishersurface preparation device. It should be understood, however, that theycan be equally applied to a number of other surface preparation devicessuch as sanders or road surface preparation machines.

The term “surface preparation” as used herein may refer to levelling,polishing, grinding, cleaning, removing resins/lacquers/paint or thelike, slicing, shredding and scraping. The term “grinding” will becommonly used to refer to any type of surface preparation employing anabrasive/frictional treatment step.

FIG. 1 is a perspective view of the underside of a surface preparationdevice 10 employing a plate locking mechanism 50 according to anembodiment of the invention. The surface preparation device 10 may beany concrete grinder, floor polisher, sander etc of a type commonly usedin the industry. Non-limiting examples of such surface preparationdevices 10 are those commercially available from Polivac InternationalPty Ltd (such as a Polivac PV 25 floor polisher with a brush speed of420 rpm, a Polivac SV 30 with a brush speed of 350 rpm or a Polivac SV25sander with a brush speed of 192 rpm) or Rotavac. The housing, body andinner workings of the surface preparation device 10, per se, are not thesubject of the present invention and will generally be of a standardtype well known to those skilled in the art of surface preparation.

Surface preparation device 10 has a housing 11 and travels along ongrinding discs 21 when driven by an operator pushing on handle 12. Theunderside of surface preparation device 10 reveals a rotatable plate 20onto which are attached surface preparation tools in the form of thegrinding discs 21. Rotatable plate 20 has a cylindrical through hole oraperture in its centre formed by a plate collar 22 of which the interiorwall can be viewed in FIG. 1. At the internal upper extent of platecollar 22 is located plate locking mechanism 50 which operates to holdrotatable plate 20 in position during use. FIG. 2 provides furtherdetail.

FIG. 2 is an exploded view of the components of the plate lockingmechanism 50, according to an embodiment of the invention, withassociated rotatable plate 20 and accessories. Rotatable plate 20 has,in the embodiment described, three grinding discs 21 attached to itsgrinding surface which will, during operation, contact and grind thesurface being prepared. Grinding discs 21 may be metal structures withabrasive material such as sand paper, stones, silicon carbide or diamondtips. On the opposite surface to the grinding surface, rotatable plate20 has a plate collar 22 projecting generally upwards from the plane ofthe rotatable plate 20 to define a hollow interior forming a cylinderwhich is continuous with an aperture in the grinding surface ofrotatable plate 20 of equal diameter.

Rotatable plate 20 is also provided with a disc attachment aperture 23for each grinding disc 21 which, in use, is in alignment with a grindingdisc aperture 24 formed in each grinding disc 21. These alignedapertures, 23 and 24, receive a grinding disc fastener 25 to hold thegrinding disc 21 firmly in place but may, if required, allow forrotation of grinding disc 21. In the embodiment shown, the grinding discfasteners 25 take the form of a mandrel and, advantageously, mandrels 25may be magnetic mandrels. Mandrel head 26 can be seen abutting the uppersurface of rotatable plate 20 to prevent the associated grinding disc 21from inadvertently detaching. The use of magnetic mandrels 25 enablesthe grinding discs 21 to be attached and removed quickly and easilywhich can save considerable time when abrasives of progressively finermaterial need to be used to achieve a sufficiently smooth finish.

Rotatable plate 20 is further provided with a number of ballastattachment apertures 27 to enable the placement and attachment ofweights as ballast 28 onto rotatable plate 20 to provide for anincreased grinding force. Ballast fastener 29, which may be a simplebolt or the like, is used to pass through an aperture formed in theballast 28 (not shown) and the ballast attachment aperture 27 to fastenthe ballast 28 to the rotatable plate 20. It is a distinct advantage ofthe present invention that ballast 28 is able to be carried on therotatable plate 20 rather than placed on the housing 11 of the surfacepreparation device 10 or built into the device 10 itself. The platecollar 22 provides sufficient clearance between the rotatable plate 20and the underside of the surface preparation device 10 to allow theballast 28 to be placed there between and the plate locking mechanism ofthe present invention allows rotatable plate 20 to effectively float (aswill be described in detail herein) which means the ballast 28 can bebetter supported and much more effectively put to use.

Although, for the sake of clarity, connecting plate 30 is shown in thefigures as being separate to the plate collar 22 it will preferably beintegrally formed with or may be in some manner permanently attachedonto the rim of plate collar 22 nearest the surface of rotatable plate20 having no grinding discs 21, to form a partial cover over the hollowcylindrical interior formed inside plate collar 22. Connecting plate 30may be welded, bolted or otherwise fixed onto the upper rim of platecollar 22 and is provided with a receiving aperture 31 which is shapedso as to form blocking members 32 which, in the embodiment shown, takethe form of projecting wedges, this results in a pattern whereby ablocking member 32 is adjacent cut away portions on either side thereof.Connecting plate 30 forms a component of the plate locking mechanism 50of the invention.

Plate locking mechanism 50 further comprises a locking base plate 51which is shaped so as to compliment the shape of receiving aperture 31and is capable of being located therein. The locking base plate 51 has acentral aperture 52 formed in its body 55 and radial apertures 53 formedin projecting members 54 which radiate from the body 55 of locking baseplate 51. The alternating pattern of projecting members 54, in the formof wedges, and cut away portions mirrors that of connecting plate 30 sothe two can fit together to form one solid plate, ignoring therelatively small apertures in the locking base plate 51. The thicknessesof locking base plate 51 and connecting plate 30 are substantially thesame so that, when one is fitted inside the other, the surfaces of thetwo seen by a viewer looking at the underside of the surface preparationdevice 10, sit flush. The locking base plate 51 can be connected to theunderside of the surface preparation device 10 by means of locking basefasteners 56, which may take the form of screws, bolts or the like,passing through radial apertures 53 and connecting to any suitablystrong and rotatable component of the surface preparation device 10. Inalternative embodiments, locking base plate 51 may simply be a rotatableplate or surface already present on the underside of the surfacepreparation device 10 to which a floating plate 60 can be attached. Thepresent invention can thus not only be incorporated into new surfacepreparation devices 10 but is capable of being retrofitted to existingdevices with a minimum of modification.

Floating plate 60 has a contact surface which sits in contact withlocking base plate 51 and this surface has a shape which substantiallyconforms to that of plate 51. The surface of floating plate 60 oppositeto that in contact with locking base plate 51 is provided with anactuator in the form of a handle 61 in which there may be provided ahandle aperture 62 (as shown more clearly in FIG. 3). Located beneaththe handle 61 is a fastening member 63 in the form of a bolt having anat least partially threaded shank 64 around which is placed a resilientor dampening member 65 which, in the embodiment shown, takes the form ofa spring such as a compression spring. The resilient member 65 may takea range of other forms which would be known to a skilled addressee suchas various designs of spring or solid rubber and/or polymericcompressible bodies so long as the material used can withstand therelatively abrasive environment of use. The threaded portion of shank 64passes through a floating plate central aperture 66 and ends in thethreaded central aperture 52 of locking base plate 51 to engagetherewith. The threaded portion of shank 64 does not actually threadedlyengage with the floating plate central aperture 66 but rather merelypasses through said aperture. The components of the plate lockingmechanism 50 can be seen in more detail in FIG. 3.

FIG. 3 is a perspective view of a plate locking mechanism 50 accordingto an embodiment of the invention. Once again, connecting plate 30 isshown separate to the rest of the rotatable plate 20 simply for the sakeof clarity. It is clear from FIG. 3 that the shapes of floating plate 60and locking base plate 51, when in alignment, will fit closely into thecomplimentary shape of receiving aperture 31 of connecting plate 30.

As discussed previously, locking base plate 51 will be fastened to theunderside of the surface preparation machine 10 at a suitable locationby locking base fasteners 56 and so it will not be free to move in anymanner. The component to which locking base plate 51 is attached (orlocking base plate 51 itself) will be the normal component of the devicewhich is rotatable by the motor of the surface preparation device 10 tothereby ultimately effect rotation of rotatable plate 20. The contactsurface of floating plate 60 will be maintained in direct contact withlocking base plate 51 unless a pulling force is exerted on handle 61 andso, once floating plate 60 and locking base plate 51 are in place andaligned, the connecting plate 30, and attached rotatable plate 20, willbe appropriately located by lifting the rotatable plate 20 such thathandle 61 enters first through receiving aperture 31 until locking baseplate 51 is located within receiving aperture 31 and the visiblesurfaces of connecting plate 30 and locking base plate 51 aresubstantially flush with one another. The rotatable plate 20 is then inplace and ready to be locked.

The floating plate central aperture 66 is not threaded and does notengage, as such, with the threaded shank 64 of bolt 63 but rather thefloating plate 60 is maintained in forced contact with the surface oflocking base plate 51 by the compression force created by resilientmember 65. This force is generated as bolt 63 will be screwed into andtherefore engaged with locking base plate 51 to a sufficient extent tohave the head or associated washer thereof compress the resilient member65 which transmits this force to the surface of floating plate 60 whichit contacts thereby forcing floating plate 60 into contact with lockingbase plate 51. The extent to which bolt 63 is tightened will determinethe force transmitted to floating plate 60 and hence will determine theextent of the dampening effect created when forces from rotatable plate20 try to work against this effect.

In one embodiment the invention resides in a plate locking mechanism fora surface preparation device comprising:

-   -   (a) a connecting plate having a receiving aperture and at least        one blocking member;    -   (b) a base plate having a base plate aperture, the base plate        accommodated within the receiving aperture;    -   (c) a floating plate in contact with and capable of being        substantially aligned with the base plate, the floating plate        having at least one floating plate projection and a floating        plate aperture;    -   (d) a fastener extending through the floating plate aperture and        engaging with the base plate aperture; and    -   (e) a resilient member adapted to exert a force on a surface of        the floating plate;

wherein, rotation of the floating plate to align the at least onefloating plate projection with the at least one blocking member causesthe connecting plate to be retained.

Preferably, the resilient member is operatively associated with thefastener.

Suitably, the resilient member is a spring through which the fastenerpasses.

The fastener being located further into the base plate aperture causesthe resilient member to be compressed to a greater degree. Compressionof the resilient member to a greater degree increases the force exertedon the surface of the floating plate. The force exerted by the resilientmember on the surface of the floating plate works against the forceexerted by the weight of the connecting plate on the floating plate.

FIG. 4A is a perspective view of a plate locking mechanism 50, accordingto an embodiment of the invention, when in the unlocked/removalconfiguration. The floating plate 60 and locking base plate 51 are inalignment and they, together, have been inserted into the receivingaperture 31 of connecting plate 30, as described in relation to FIG. 3.The view shown in FIG. 4 makes it clear that when floating plate 60 andlocking base plate 51 are in alignment then the heads of locking basefasteners 56 are accommodated within floating plate apertures 68, formedin floating plate projections 67, which thereby prevents any rotationalmovement of floating plate 60.

This position shown in FIG. 4A represents the situation whereby lockingbase plate 51 has been fastened to the underside of the surfacepreparation device 10 and the connecting plate 30 with attachedrotatable plate 20 (not shown for the sake of clarity) has been slippedover handle 61 and locking base plate 51 sits flush within receivingaperture 31. It can be seen that, since locking base plate 51 andconnecting plate 30 are of the same thickness, floating plate 60 sitsabove the surface of connecting plate 30. From the position shown theuser is ready to lock rotatable plate 20 and connecting plate 30 inplace.

FIG. 4B is a perspective view of the plate locking mechanism 50,according to an embodiment of the invention, when in thelocked/operational configuration. In moving from the position shown inFIG. 4A to that in FIG. 4B the user is required to lift handle 61 which,since it is integrally formed or attached to floating plate 60, resultsin floating plate 60 moving away from the surface of locking base plate51 in which it was in contact with and in resilient member 65 beingcompressed. The user needs to raise floating plate 60 in this manner toa point whereby floating plate projections 67 are above the level of theheads of locking base fasteners 56 and then apply a twisting or rotatingmotion to handle 61 to rotate floating plate 60 with respect to bothshank 64 of bolt 63 and locking base plate 51. This results in floatingplate projections 67 being located between the heads of locking basefasteners 56 at which point the user can release handle 61. The lockingbase fasteners 56 prevent rotation of the floating plate 60 fromreaching the point where floating plate projections 67 would be inalignment with projecting members 54 and so the rotatable plate 20 wouldbe released. The locking base fasteners 56 thereby act not only to affixlocking base plate 51 to the surface preparation device 10 but also tomaintain the plate locking mechanism in the locked/operational position.

It will be appreciated that, at this point, the blocking members 32 ofconnecting plate 30 are now trapped behind and are at least partially incontact with the face of floating plate projections 67 which waspreviously in contact with the projecting members 54 of locking baseplate 51. This is the operational configuration as rotatable plate 20(which is integral with or attached to connecting plate 30) is now heldin place on the underside of surface preparation device 10 and locked inthat position by the configuration of the floating plate 60. The lockingbase plate 51 and floating plate 60 are, in this operationalconfiguration, located within the hollow cylindrical aperture defined bythe walls of plate collar 22. This can be seen in FIG. 1. Grinding discs21 can then be placed in position on rotatable plate 20 and the user isready to commence the surface preparation treatment, such as grinding ofa cement floor.

When the treatment is complete and the user wishes to remove rotatableplate 20 or wants to add or remove ballast 28 there from then, startingfrom the position shown in FIG. 4B, handle 61 is lifted and rotateduntil the heads of locking base fasteners 56 are aligned with floatingplate apertures 68 at which point the handle 61 is released and theunlocked or removal position shown in FIG. 4A has been achieved. Therotatable plate 20 is then easily removed for adjustment andre-attachment or storage.

The system described above presents a number of advantages over theprior art. Firstly, once locking base plate 51 has been permanentlyattached to the underside of the surface preparation device 10 thenattaching and removing the rotatable plate 20 is a simple matter ofpulling and twisting handle 61 to switch between the locked and releaseconfigurations. This results in major time savings during jobs such asconcrete polishing where, to grind the surface to a fine finish, a rangeof different grade grinding discs 21 and ballast 28 may need to be addedor removed from rotatable plate 20 or indeed different size or weightrotatable plates 20 employed. This regular changing necessitatesfrequent removal of rotatable plate 20 and so any mechanism whereby thechangeover can be speeded up can result in time and cost savings for theoperator.

Secondly, and importantly, the design shown provides a dampening effectto bumps and vibrations caused by an uneven surface during surfacepreparation. The manner or angle in which grinding discs 21 are held orpresented to the surface to be prepared by rotatable plate 20 iscritical during surface preparation. Changes in this angle due to anuneven surface can result in a more aggressive cutting or grindingaction than is desirable and may permanently damage the surface. Thepresent invention provides a system whereby the rotatable plate 20 isnot held in an absolute fixed position but rather, due to the resilientmember 65 and the manner in which it is suspended from the underside ofthe device 10 by locking mechanism 50, it can flex and re-orient itselfin response to the particular contours of the surface being treated.This effect will be described in more detail below.

When in the locked configuration shown in FIG. 4B the rotatable plate 20is effectively hanging from the underside of the surface preparationdevice, suspended by the overlapping engagement of blocking members 32of connecting plate 30 with the floating plate projections 67 offloating plate 60. The floating plate 60 would be forced towards thepreparation surface by its own weight if it were not for the resistiveforce it receives from compression spring 65 which is held in place bythe head and associated washer of bolt 63 which is engaged at itsthreaded shank 64 portion with locking base plate 51. When bumps or dipsare encountered during operation on the surface being treated then therotatable plate 20 will be caused to tip to one side or another. Theforce caused by this shift is transmitted to the floating plateprojections 67 which are caused to push against compression spring 65and further compress it. The compression spring 65 will allow thisslight movement but will dampen the shock of the force and then returnto its normal state once the additional force felt by rotatable plate 20ends. This action provides for uneven surfaces to be accommodated byenabling rotatable plate 20, and hence attached grinding discs 21, tomove to the necessary extent while dampening the jerking or sharp motioncaused by uneven surfaces which can result in overly aggressive grindingand surface damage.

A further advantage of the flexibility achieved by the use of floatingplate 60 and resilient member 65 is that the surface preparation device10 is easier for the operator to manoeuvre. A relatively slight pressurewill result in a movement of floating plate 60, as described above, andthe device 10 will follow that movement while it is maintained. Lesseffort is asked of the operator to move the device 10 from side to sideand it is easier to control thereby enabling a better finish to beachieved with less physical exertion. This is a great improvement overprior art machines which could not always be operated by those of aslight build and were more prone to unexpected or undesired movementsproviding a less than ideal finish.

Further, the easy attachment and removal of the rotatable plate 20coupled with the design of rotatable plate 20 itself allows the ballast28 to be connected directly to rotatable plate 20 rather than to thehousing 11 of the surface preparation device 10. This makes it easier toseparate out the weight of the machine from the weight of the ballastallowing them to be separated for easier and safer lifting andtransport. Importantly, this also reduces wear and tear on the surfacepreparation device itself as the rotatable plate 20 is made to bear theweight of ballast 28 and thereby takes on much of the actual work of thedevice 10 in grinding the surface to be prepared. The provision of asystem which enables the grinding plate in contact with the preparationsurface via the grinding tools, i.e. rotatable plate 20 and grindingdiscs 21, to hang and float more or less free of the body of the surfacepreparation device 10 is a significant advantage as all of the adjustingto the surface being prepared, the jolts from bumps etc and theresistance encountered at the preparation surface are all passed ontorotatable plate 20 and hence to resilient member 65 thereby reducing thework required from and wear and tear caused to the surface preparationdevice 10 as well as making it considerably easier for the user tocontrol the device 10 during these events. Due to the advantagesprovided by the floating effect described it is preferred that thepresent invention is used with surface preparation devices 10 which donot have wheels or have wheels which are removable. This is because thepermanent raised support provided by a set of wheels reduces theeffectiveness of the floating support system due to a reduced contactwith the surface being prepared.

In one embodiment the invention lies in a rotatable plate for a surfacepreparation machine comprising a plate collar defining a hollow passage,the collar extending generally upwards from the plane of the rotatableplate and ending in a connecting plate having a receiving aperturecontinuous with the hollow passage.

Preferably, the collar extends a sufficient distance above a surface ofthe rotatable plate to accommodate a locking mechanism within the hollowpassage thereby formed.

Suitably, the receiving aperture is of a complimentary shape to alocking base plate which can be accommodated therein. The rotatableplate will be provided with disc attachment apertures and/or ballastattachment apertures for the attachment of grinding tools and weights,respectively. The grinding tools may be attached to the rotatable plateby means of fasteners such as magnetic mandrels. The use of magneticmandrels means the grinding tools can be removed and replaced with greatefficiency.

It will be appreciated that the plate locking mechanism 50 may beconsidered to include connecting plate 30 of rotatable plate 20 sincethe receiving aperture 31 of connecting plate 30 must accommodate theshape of locking base plate 51 for the locking mechanism to successfullywork but it is the combination of locking base plate 51, to attach tothe surface preparation device 10, and floating plate 60, with resilientmember 65, which effects the actual locking action. The connecting plate30 will generally be integrally formed with or permanently attached tothe rotatable plate 20 and so the inventive solution offered is sharedby the rotatable plates and the other locking mechanism components dueto their interworking relationship defined by their complimentary shapesand working engagement.

The skilled addressee will appreciate that the present invention is notlimited to the particular shapes of connecting plate 30, receivingaperture 31, locking base plate 51 and floating plate 60 shown in FIGS.1 to 4B. Other shapes may also be suitable and, indeed, may provideparticular advantages of their own, as is discussed below.

FIG. 5 is a perspective view of a plate locking mechanism 100 accordingto a further embodiment of the invention. This plate locking mechanism100 works in essentially the same manner as described above but theshapes of the components have been altered from the wedge-shapedblocking members 32, projecting members 54 and floating plateprojections 67 to take on a clover-shaped design whereby each individualprojection is circular at its border.

Connecting plate 101 has a receiving aperture 102 and blocking members103 which resemble rounded peak-like projections. Locking base plate 110has three projecting members 111, a central aperture 112 and a number ofradial apertures 113 to receive fasteners which will attach the lockingbase plate 110 to the underside of the surface preparation device 10.Floating plate 120 has floating plate projections 121, floating plateapertures 122 and floating plate central aperture 123 which is threadedand engages with the complimentary threaded portion of bolt 125. Handle126 is integrally formed on a surface of floating plate 120 which doesnot contact locking base plate 110 and resilient member 127, in the formof a compression spring, is located around bolt 125.

As in the embodiment discussed previously, the contacting surfaces offloating plate 120 and locking base plate 110 are substantially similarin shape and dimension and so can be aligned with one another withoutany substantial overlap. Their shape is complimentary to that ofreceiving aperture 102 and so locking base plate 110 can be locatedtherein and the rotatable plate (not shown but integral with connectingplate 101) attached and removed as already described.

The main difference achieved by the alteration in shape from the wedgedesign to the clover leaf design is the differing manner in which thefloating plate moves in response to movement transmitted from therotatable plate. The clover-leaf design shown in FIG. 5 allows for aslightly more pronounced circular movement of the rotatable plate whichwill advantageously suit certain users and certain surface types.

FIG. 6 is a perspective view of a plate locking mechanism 200 accordingto yet a further embodiment of the invention. This plate lockingmechanism 200 works in essentially the same manner as described abovebut this time the shapes of the components have been altered from thewedge-shaped or clover-leaf design to take on an X-shaped orcross-shaped design whereby each individual projection is reminiscent ofthe upper and side faces of a pentagon.

Connecting plate 201 has a receiving aperture 202 and blocking members203 which are triangular in shape. Locking base plate 210 has fourprojecting members 211, a central aperture 212 and a number of radialapertures 213 to receive fasteners which will attach the locking baseplate 210 to the underside of the surface preparation device 10.Floating plate 220 has floating plate projections 221, floating plateapertures 222 and floating plate central aperture 223 which is threadedand engages with the complimentary threaded portion of bolt 225. Handle226 is integrally formed on a surface of floating plate 220 which doesnot contact locking base plate 210 and resilient member 227, in the formof a compression spring, is located around bolt 225.

As in the embodiments discussed previously, the contacting surfaces offloating plate 220 and locking base plate 210 are substantially similarin shape and dimension and so can be aligned with one another withoutsubstantial overlap. Their shape is complimentary to that of receivingaperture 202 and so locking base plate 210 can be located therein andthe rotatable plate (not shown but integral with connecting plate 201)attached and removed as already described.

As with the embodiment shown in FIG. 5, the main difference achieved bythe alteration in shape of the various projections, blocking members andreceiving aperture is the differing manner in which the floating platemoves in response to movement transmitted from the rotatable plate. Thedesign shown in FIG. 6 may serve to provide additional stability to therotatable plate when operating at higher rpm's.

FIGS. 7A to 7D are plan views of a number of alternative designs 310,320, 330 and 340 for use in forming a plate locking mechanism accordingto various embodiment of the invention. Each embodiment is a view of alocking base plate accommodated within a connecting plate and so foreach design the floating plate would be underneath (obscured in thisview) the locking base plate and would have a substantially similarshape to that plate, as with the embodiments described above. Thesealternative designs each provide their own advantage in terms of thedampening effect they provide and the experience the operator feels whendriving the device 10. 310 represents a locking base plate and floatingplate structure whereby their projections are squared off in shape onextending from the central portion, 320 represents a three-prongedpentagon shape of projections, 330 represents a simple triangle with cutoff points and 340 represents a similar situation to 310 but with eachof the faces of the square projections having been curved (outwards i.e.convex at the outermost and inwards i.e. concave at the sides).

Throughout the specification the aim has been to describe the preferredembodiments of the invention without limiting the invention to any oneembodiment or specific collection of features. It will therefore beappreciated by those of skill in the art that, in light of the instantdisclosure, various modifications and changes can be made in theparticular embodiments exemplified without departing from the scope ofthe present invention.

1. A plate locking mechanism for a surface preparation devicecomprising: (a) a connecting plate having a receiving aperture and atleast one blocking member; (b) a base plate having a base plateaperture, the base plate having a shape complimentary to that of thereceiving aperture; (c) a floating plate capable of being substantiallyaligned with the base plate, the floating plate having a first surface,at least one floating plate projection and a floating plate aperture,the first surface in contact with the base plate; (d) a fastenerextending through the floating plate aperture and engaging with the baseplate aperture; and (e) a resilient member operatively associated withthe fastener and in compressing contact with a second surface of thefloating plate; wherein, location of the base plate within the receivingaperture enables the floating plate to be rotated to align the at leastone floating plate projection with the at least one blocking member tothereby lock the connecting plate in position.
 2. The plate lockingmechanism of claim 1 wherein the connecting plate is connected to arotatable plate comprising a grinding tool.
 3. (canceled)
 4. The platelocking mechanism of claim 1 wherein the connecting plate is integralwith the rotatable plate.
 5. The plate locking mechanism of claim 1wherein the floating plate further comprises an actuator.
 6. The platelocking mechanism of claim 1 wherein the base plate comprises at leastone projecting member extending from a body thereof.
 7. The platelocking mechanism of claim 6 wherein the at least one floating plateprojection can be aligned with the base plate at least one projectingmember.
 8. The plate locking mechanism of claim 6 wherein the base plateat least one projecting member is adapted to be accommodated within acomplimentary portion of the receiving aperture.
 9. The plate lockingmechanism of claim 1 wherein the fastener threadedly engages with thebase plate aperture.
 10. (canceled)
 11. The plate locking mechanism ofclaim 1 wherein the resilient member is a compression spring throughwhich the fastener passes.
 12. The plate locking mechanism of claim 11wherein movement of the fastener further into the base plate aperturecauses compression of the compression spring and increases the forcemaintaining the first surface of the floating plate in contact with thebase plate.
 13. The plate locking mechanism of claim 6 wherein the baseplate at least one projecting member comprises a radial aperture toreceive a locating fastener.
 14. The plate locking mechanism of claim 13wherein a head of the locating fastener can be accommodated within afloating plate aperture formed within the at least one floating plateprojection.
 15. The plate locking mechanism of claim 14 wherein theactuator is moved in a direction away from the base plate to place thefloating plate above the level of the head of the locating fastenerprior to rotation of the actuator. 16-27. (canceled)
 28. A plate lockingmechanism for a surface preparation device comprising: (a) a floatingplate having an actuator, at least one floating plate projection and afloating plate aperture; (b) a fastener extending through the floatingplate aperture, the fastener having a head and a shank and being adaptedto engage a base plate; and (c) a resilient member at least partiallysurrounding the shank and extending between the head of the fastener anda receiving surface of the floating plate; wherein, moving the head ofthe fastener towards the receiving surface of the floating platecompresses the resilient member.
 29. The plate locking mechanism ofclaim 28 wherein the floating plate has a plurality of floating plateprojections extending from a central body.
 30. (canceled)
 31. The platelocking mechanism of claim 28 wherein the resilient member is acompression spring through which the fastener passes.
 32. (canceled) 33.(canceled)
 34. A rotatable plate for a surface preparation devicecomprising a plate collar defining a hollow passage, the plate collarextending generally perpendicularly from the plane of the rotatableplate and ending in a connecting plate, the connecting plate in a planeparallel to that of the rotatable plate and having a receiving aperturecontinuous with the hollow passage.
 35. The rotatable plate of claim 34wherein the plate collar extends above a surface of the rotatable plateto accommodate a plate locking mechanism within the hollow passage. 36.The rotatable plate of claim 34 wherein the receiving aperture isadapted to accommodate a base plate having a shape complimentary to thereceiving aperture.
 37. The rotatable plate of claim 34 furthercomprising disc attachment apertures and/or ballast attachment aperturesfor the attachment of grinding discs and weights, respectively. 38.(canceled)